Shield for cathode ray tubes



March 7, 1944. w JR 2,343,630

SHIELD FOR CATHODE RAY TUBES Filed April 25, 1942 My 7 Y INVENTOR.

ll TTORNEY Patented Mar. 7, 1944 SHIELD FOR CATHODE RAY TUBES HoraceAtwood, Jr., Passaic, N. 1., assignor to Allen 13. Du Mont Laboratories,Inc., Passaic. N. J., a corporation of Delaware Application April 25,1942, Serial No. 440,453

3 Claims.

This invention relates to a shield for a cathode ray tube which shieldsthe tube from magnetic as well as electrostatic influences. It isprimarily for the purpose of shielding the electron beam of the tubefrom both magnetic and electrostatic stray fields so that errors ofdeflection of the beam will be avoided.

In carrying out the invention an electrostatic and magnetic shield ofhigh magnetic permeability is applied to the outside surface of thecathode ray tube in such a way that it does not in any way interferewith the normal operation of the tube or add very materially to the costthereof.

The invention may be understood from the description in connection withthe accompanying drawing which is a side view of a cathode ray tubeshowing in section a magnetic and electrostatic shield applied to thetube.

In the drawing reference character I indicates a cathode ray tube havingthe usual metallic base 2 with center pin 3 and a circular row ofcontact pins 4. The structure inside the tube for generating anddeflecting the cathode ray may be made up of any of the known sorts.They are not shown as they do not constitute any part of this invention.The external portion of a connector for making electrical connectionfrom a source of high potential to the customary intensifier for thecathode ray beam located inside the tube is shown at 5.

The magnetic and electrostatic shield 6 for the tube i is applied to theouter surface thereof and is shown in section by the cross hatching. Itis applied to the tube I from a region at or near the metal base 2nearly to the outer or large end of the tube. A hole I is providedthrough the shield 6 so that it will not contact with the connector 5. Ametal Jumper or band 8 connects the shield 6 electrically to the metalbase 2.

The shield Bis made up of finely granulated material of high magneticpermeability in weak magnetic fields. This material is also of goodelectrical conductivity. For example, particles of mu metal, which is analloy of iron and nickel, or pure iron. or other magnetically permeableand electrically conductive material may be used for preparing theshield 6.

The metallic material for the shield 6 is finely divided ordisintegrated and suspended in a binder and the suspension is applied toor coated upon the outer surface of the cathode ray tube l in anyconvenient way as by brushing or spraying it on, for example, until asufilciently thick layer is provided to exclude magnetic fields 0f theorder of 0.5 gauss. Thicknesses of 0.15 inch have been found to besuflicient in most cases. The suspension material or binder to be usedmay be of a variety of materials such as a Celluloid base binder,synthetic resin, asphalt, etc., that will adhere to the surface of thetube and retain the metallic particles in place. The amount of the metalparticles in the binder is sufiiciently large to cause enough contact ofthe particles with each other to make the coating 8electricallyconductive.

What is claimed is:

1. A magnetic and electrostatic shield for a cathode ray tube having ametal base, comprising particles of electrically conductive material ofhigh magnetic permeability applied in an adhesive binder to said tube.said shield being separated from but electrically connected to the metalbase of said tube.

2. A magnetic and electrostatic shield of high magnetic permeability fora cathode ray tube having a metal base, comprising a thick coating ofparticles of electrically conductive material of high magneticpermeability applied in an adhesive bihder to said tube, the amount ofsaid particles in said binder being sufllcient to make the shieldelectrically conductive, said shield being separated from butelectrically connected to said metal base.

3. A.magnetic and electrostatic shield for a cathode ray tube having ametal base, comprising a coating of enough particles of electricallyconductive material of high magnetic permeability in an adhesive binderon said tube to make the coating electrically conductive, said shieldbeing separated from but electrically connected to said metal base.

HORACE ATWOOD, Jn.

